In conventional non-destructive imaging systems, short pulse duration is critical for resolving anomalies existing in a test area. If the pulse duration is too long, near surface anomalies are eclipsed while the receiver waits for the transmit event to complete. Similarly, the ability for the system to distinguish between two or more anomalies along the same trajectory is dependent on a sufficiently narrow pulse. Unfortunately reducing pulse duration is not without its consequences. A narrow pulse has less detectable energy for the test equipment to reliably recover from the test site. The problem worsens as the excitation beam diverges and returns lower recoverable energy levels in proportion to increasing scan depth, lowering the SNR. This divergence over distance also increases the probability of exciting off-path reflection sources. Inadequate lateral scan line resolution can yield non-existent irregularities or ghosts that present themselves as actual in-line anomalies in regions where multiple reflection paths interact outside the path of interest and return to the receiver. A compromise must be reached that satisfies the SNR limits of the test equipment while attaining the desired scan resolution.
At present a partial solution will employ pulse compression techniques and/or array focusing to achieve the higher energy levels as with a longer pulse while partitioning the energy such that it maintains the resolution of a short pulse. However pulse compression does not unveil the anomalies existing in the near surface blind region created by the longer transmit event. A further drawback is the increased complexity at high voltage levels makes implementations more costly. At present resolutions are improved by changing to a probe that uses a smaller per-element excitation surface area whether in a single element device or a multi-element phased array. Therefore there is a need for an improved imaging system and method using improved modulated excitation.